Horizontal agitators for use in large vats or tanks are generally comprised of a drive motor and an extended shaft assembly with an impeller mounted at the inboard end of the shaft. These agitators serve to mix and stir various materials contained in the tank, depending on the application. In many instances, the USDA and other regulatory authorities are involved as the material being processed in the tank is a food grade material and can include beer, wine, milk, etc. For many years these tanks have been used and various regulations have been promulgated to require the sanitary handling of these foodstuffs. This has included a "clean-in-place" requirement for these horizontal agitators meaning that the shaft and its seals must be capable of being cleaned without removal of the agitator from the tank. Recently, these regulations have been strengthened to require that the sealing surfaces be mechanically or hydraulically separated or unseated to expose all the dynamic sealing surfaces, and that the sealing contact intersection of all seals be exposed to cleaning solutions, among other requirements. While clean-in-place agitators have previously been designed and used, these prior designs do not meet these new tougher standards. One such example is found in U.S. Pat. No. 4,511,255, the disclosure of which is incorporated herein by reference. As shown in that patent, an elongated drive shaft has an impeller at its inboard end and a bearing/seal member in an extended shaft housing comprised of a plastic plug and cylindrical passage which serves as a journal bearing for the base of the impeller. A second dynamic seal is positioned at the outer end of the drive shaft and the shaft housing. When it is desired to clean the inner seal, cleaning fluid is pumped into the shaft housing under pressure that overcomes the spring pressure that seats the outer bearing/seal members together to, ideally, unseat them and allow the cleaning fluid to flow through the shaft housing and past the seal members out into the tank. The outboard seal stays in sealing orientation and prevents the cleaning fluid from flowing back into the body of the agitator and has sealing surfaces that are neither separated or cleaned. Thus, the '255 patent device relies on fluid pressure to overcome spring force to separate only the outer bearing/seal members and permit cleaning fluid to clean their mating surfaces. Additionally, with this construction the cleaning fluid is directed to flow into the same tank where the foodstuff is contained, including the contaminants cleaned from the entirety of the extended shaft housing and the seal surfaces. This is undesirable as the contaminants are then required to be reliably washed out of the tank as well. Nor does this device provide a mechanical separation of the sealing surfaces.
In order to remedy the shortcomings of the prior art and to provide an agitator with a shaft and seal assembly that uses a mechanical force to truly and reliably separate the seal members, the inventors herein have succeeded in designing and developing the present invention in its various embodiments. Not only are the problems of the prior art resolved, but additional advantages are provided that were previously not provided. In a first embodiment of the present invention, a spring retainer and spring are mounted onto the agitator shaft and urge a dynamic seal member against a second seal member which seats against the tank sidewall. An "O" ring seals the first dynamic seal member to the shaft. All of these components are located inside the tank, with the agitator shaft extending through a hole in the tank sidewall. An "O" ring, or "pusher", is circumferentially mounted on the outboard end of the agitator shaft, outboard of the seal components, and positioned to be located outside the tank. When cleaning of the seal is desired, the agitator shaft is pushed into the tank far enough to bring the pusher "O" ring into mechanical contact with the second seal member to physically separate it from the tank sidewall where it might otherwise tend to remain due to any accumulation of foodstuff or as a result of the compressive forces of the spring against it. Then, cleaning fluid is sprayed onto the shaft from inside the tank, as all of the seal components including the pusher are physically positioned inside the tank. This eliminates the dumping of cleaning fluid and contaminants into the tank. Some cleaning solution will flow past the second seal member and out of the tank.
In a second embodiment of the present invention, an elastomeric "plug" is slidably mounted onto the agitator shaft and it has a seating surface against which a fixed, matching seal member bears to urge it into a hole in the tank sidewall. Thus, as the shaft turns, the elastomeric portion remains in static seal with the tank sidewall and the inboard end serves as a sealing surface for the matching seal member against which it rotates. Outboard of the elastomeric plug, and positioned outside the tank, is a circumferentially mounted "pusher" which has a profile to engage the elastomeric plug and physically separate it from the tank sidewall as the agitator shaft is pushed into the tank for cleaning. The elastomeric portion of the seal member, when compressed, provides the sealing pressure to maintain the seal against the tank. As with the first embodiment, all but the pusher member is located inside the tank during operation. Also, the elastomeric member may have a cylindrical shoulder which helps to close off the tank opening as the cleaning fluid is sprayed so as to minimize the amount of fluid and contaminant that flows out of the tank. A further advantage is that the seal construction eliminates the use of a coiled spring, which simplifies the design and makes it less expensive and more sanitary.
A third embodiment of the present invention is somewhat different from the first two embodiments and provides additional advantages even beyond that offered by the first two embodiments. With this embodiment, the agitator shaft need not be moved to separate the seal for cleaning. Also, the spring member is positioned outside the tank. More particularly, a rotary seal member is fixed to the inboard of the agitator shaft so as to be located inside the tank. A rotary seal disk is slidably mounted adjacent the rotary seal member and provides the surface against which the dynamic seal is formed. The rest of the seal is contained inside a housing which is mounted to the outside of the tank. This includes a spring loaded, nose shaped seal member which extends through a hole in the tank and which is urged against the rotary seal disk by the springs. A dynamic seal is formed between these two seal members. The spring loaded seal member may be retracted by mechanically withdrawing it from inside the tank hole, and an "O" ring pusher mounted on the agitator shaft engages the rotary seal disk should it not readily separate from the nose shaped seal member and mechanically separates it therefrom. With this embodiment, the cleaning fluid may be sprayed from inside the tank and allowed to flow outside the tank, carrying the seal contaminants with it. This embodiment is perhaps not as mechanically simple or elegant as the other embodiments, but the other advantages offered by it may be important enough to consider it for any particular application.
While the principal advantages and features of the present invention have been briefly explained above, a greater understanding may be attained by referring to the drawings and description of the preferred embodiment which follow.